The invention relates to a universal-joint tool head as a unit which may form part of various milling-machine designs and is set up to move in the linear axes X, Y, Z.
There are various types of milling machines with milling-head units with two continuously movable axles, for example milling-head units with an angle-pin head or with a fork head. DE 34 07 679 C1 has described a horizontal drilling and milling unit with a spindle head which can pivot about a pin which is inclined at 45xc2x0 to the horizontal, can be locked in the horizontal and vertical working positions of the drilling spindle sleeve with a supporting housing and in which the spindle sleeve can be driven by means of a bevel gear mechanism.
Furthermore, U.S. Pat. No. 3,483,796 A has described a milling-head unit with a fork head, in which the fork head is allowed to pivot through up to 90xc2x0 and to rotate about a pin which is perpendicular thereto. In these known milling-head units, the milling cutter spindle is driven through a spindle bar which can be adjusted in the X, Y and Z directions by means of intermediate gears which are responsible for the pivotability of the spindle head and the drive in each angular position. Servomotors effect the adjustment in the X, Y and Z directions. The supply of cooling lubricant and power to the spindle takes place via rotary leadthroughs, and the measurement-system signals are transmitted via slip rings. The housing components are generally made from steel. The spindle bar is mounted either hydrostatically or by means of rolling-contact bearings. These known milling-head units take up large amounts of space, have a high mass and problems with sealing the supply of cooling lubricant to the spindle. The known systems are difficult to assemble, the manufacturing costs are high and the maintenance outlay is considerable.
The reference book xe2x80x9cWerkzeugmaschinenxe2x80x9d [Machine tools] by Manfred Beck, Springer-Verlag 1998, pages 203 to 209, describes more recent machine tool designs based on the HEXAPOD principle, operating on the basis of a bar mechanism. One of the machines described has six stilts, the length of which cannot be changed and of which in each case two can be displaced vertically on a frame which has three stands. The tool unit is manipulated through displacement of the points where the bars are articulatedly attached to the frame. The rigid bars are mounted by means of ball and cardan joints in the drive carriages which are vertically displaceable on the frame and in which the primary parts of linear drives are integrated. In each case two primary parts which can be displaced independently of one another make use of a common secondary part. The points where the bars are articulatedly mounted on the tool unit are designed in such a way that in each case three bars engage on the front area and three on the rear area of the tool unit. Owing to the arrangement of the tool unit on three pairs of bars, control requires six degrees of freedom, even though only five degrees of freedom are required to machine workpieces on all sides by means of a milling head. For this reason, control outlay is unnecessarily high. Furthermore, the arrangement of the tool unit on bars which can be displaced by means of carriages on vertical stands limits the possible working space. However, compared to conventional milling-machine designs, the HEXAPOD principle has the advantage of a compact design for the tool unit with a low mass, so that rapid accelerations are possible. Furthermore, the HEXAPOD design provides a high level of system strength.
The invention is based on the problem of avoiding the drawbacks of the known milling-machine designs with milling-head units, making use of the advantages of the HEXAPOD principle and improving this principle in such a way that, by dint of the reduced requirements in terms of components and space, the omission of additional gear components and rotary leadthroughs and the reduction in the number of components, it is possible to reduce the construction and maintenance outlay and the moving masses, so that higher accelerations of the driven shafts and a lower outlay on control engineering can be achieved.
Working on the basis of this problem, it is proposed to equip the universal-joint tool head with a tool platform which can move in three axes, two pivoting axes and one linear axis, at least three connecting rods which are articulatedly mounted on the tool platform and can be displaced independently of and parallel to one another, at least three linear-movement drives, which are arranged at a distance from and around the tool platform and are parallel to one another, for the connecting rods which are articulatedly mounted thereon, the connecting rods being articulatedly mounted on the tool platform in such a manner that they can move on all sides and being articulatedly mounted on the linear-movement drives in such a manner that they can pivot about pins running perpendicular to the direction of movement.
Since the tool platform is mounted on connecting rods which can be displaced independently of and parallel to one another, it is possible to provide direct drives both for a motor spindle and for the pivot axes and the linear axis, and the lines for supplying cooling lubricant and power can be connected directly to the tool platform or to a motor spindle or to a milling-cutter spindle support or to a milling-cutter spindle drive without using rotary leadthroughs.
Advantageously, a motor spindle with a mount for an angle head which can be exchanged automatically from a tool magazine and can rotate in a controlled manner about the axis of the motor spindle may be arranged on the tool platform. Angle heads of this nature can be used to drill holes in different angular positions.
Preferably, the linear-movement drives may be attached to the inner surface of a tubular housing in such a way that they are parallel to one another and to the axis of the housing; the connecting rods may be designed as A-frame arms and their tips may be articulatedly mounted on the tool platform in such a manner that they can move on all sides, while their bases may be articulatedly mounted on the linear-movement drives in such a manner that they can pivot about pins running perpendicular to the direction of movement of the linear-movement drives.
If the tubular housing is arranged in a spindle bar or is designed as a spindle bar and can be displaced in the axial direction, and the spindle bar is arranged on a vertically adjustable carriage 26 which is guided on a stand 25, the stand and the workpiece 27 being displaced relative to one another, very large workpieces can be machined in the same way as with a conventional milling machine, but more quickly and with greater accuracy.
In detail, the connecting rods may be designed so as to initially run substantially obliquely in the radial direction and then, having been bent off through an angle, to run approximately parallel to the linear-movement drives, so that their pivot pins on the linear-movement drives are offset with respect to the articulation points on the tool platform.
Play-free guidance and movement control of the connecting rods is achieved if the linear-movement drives have linear direct drives or recirculating ball screw drives which are moved by servomotors.
A CNC control unit for the linear-movement drives effects the tilting of the motor milling-cutter spindle about the two pivot axes and the movement in the direction of the third linear axis, and position indicators for the connecting rods, which interact with the CNC control unit, may be integrated in the linear-movement drives.
The measurement systems which are required for the machine control unit to measure the rotation angles about the pivot axes and the displacement travel in the direction of the linear axis, can be integrated in the linear-movement drives, either as a result of suitable encoders being integrated in the corresponding drives or the drives themselves being designed as distance or rotation-angle indicators.
As a result of the tool platform being suspended from the connecting rods, the lines for the supply of cooling lubricant and power can be directly connected to the tool platform without using rotary leadthroughs and can be coupled to automatically changeable motor spindles or machining heads.
The novel design of the universal-joint tool head with the tool platform mounted on connecting rods which can be displaced independently and in parallel in the linear axis results in a reduced need for space in this direction, since there is no need for any additional gear components between the universal-joint tool head and the spindle bar. As a result, it is also possible to reduce the number of components, and the fact that rotary leadthroughs are no longer required means that a higher level of reliability and an improved seal is achieved for the supply of cooling lubricant and power. If, in addition, the housings and/or housing parts consist of a light metal alloy, of a titanium alloy and/or of foamed metal, the moving masses can be reduced still further, so that both higher accelerations in the X, Y and Z directions and higher accelerations about the pivot axes are possible, since the use of low-mass servomotors eliminates the limitations which are present in the known milling-head units.